Components of gas mixtures are frequently separated from the gas mixtures by PSA. Although PSA is generally more useful when the desired component is the least strongly adsorbed component, this gas separation technique can be successfully used when the desired component is more strongly adsorbed by the selected adsorbent than are the other components of the gas mixture. For example, carbon monoxide can be separated from gas mixtures containing, in addition to carbon monoxide, hydrogen, carbon dioxide, methane and nitrogen by means of cuprous ion-containing adsorbents. Such mixtures often occur in syngas, a hydrogen and carbon monoxide mixture produced in hydrocarbon reforming processes. It is difficult, however, to recover carbon monoxide in high purity, even using copper-modified adsorbents, because carbon dioxide, methane and nitrogen are generally coadsorbed to some degree by most adsorbents.
Certain procedures, such as cocurrently purging the adsorbent with desorbed product gas before the evacuation step, enhance the purity of the strongly adsorbed product. However, it usually requires a considerable quantity of product gas purge to obtain reasonable purity of the desorbed product gas, and even when the purge gas effluent is recycled to the feed stream, the yield of product gas is low. Process improvements which enhance the purity of strongly adsorbed product gas without sacrificing the product gas yield are continually sought. The present invention provides such an improvement.